if you want trouble free dont buy used and I would say a crf450x or the wr450 is probaly the best. the only thing with the wr is from factory you will have do some modds to really get the hp out of it. out of the box the crfx is you best bet.
I'm not a big Yamaha fan, I've had lots of problems with several of them they seem to be scared of getting wet! lol But the Honda, I'm sure they are typical Honda, just run perfect forever.
I had a crf250x and loved it and I am thinking about getting a anthoer bike and if i do it will be a crf450x the thing with honda is they are bullet proof. and the "x" is a wicked trail bike.
'06 450X has ran great for 3 seasons now, have it dual sported and ride it on the street and the dirt. put the "R" kit on it (cam, headpipe, opened up airbox, jetting kit) from day one, hasn't given a lick of trouble yet. going to do valves this spring just because.
I don't think it matters which brand you get, they all have their strong points and I don't think reliability is an issue anymore. love the e-start on the X tho....:d
Ive had my 07 CRF450R for one season now and put probably 60 hours on it and ive had no problems at all, i ride it pretty hard, and i checked my valves this winter and they were in spec. The only problem is they will eat aluminum sprockets like crazy (use steel) and the back tire life is poor... lots of torque... My buddy has an older yammy and hes had some problems with valves staying in spec. hope that helps a little
If buying a honda keep an eye on the engine oil. They have such a small volume and consume a slight amount. Keep it full and ride it. My 450 has been great. I have seen a CRF 250 R submerged under water. We brought it to my place took the carb apart cleaned the mud out, drained the water out of the tranny and engine and it fired up. I was impressed!
I have 07 WR 450 and love it. But you do have to debug it first cut down the throttle stop or replace with one from a YZ cut the grey wire,remove the muffler inner baffle.My cousin has the Honda 450 X it is also a good bike I chose the Yamaha because I got a better deal on it plus it had better bars (protapers) and wider foot pegs and a cool speedo /odometer.My buddy has the 05 version and has had no issues.I have heard the Kawasaki KLX 450 is also good.